1. Technical Field
The present invention relates to an image processing device for producing image data which represents an image to be displayed on an image display unit such as a liquid crystal panel.
2. Related Art
In displaying a rectangular image (hereinafter referred to as original image as well) on a projection surface such as screen by using a projector, there is a possibility that the image projected on the projection surface (hereinafter referred to as projection image as well) is distorted into a trapezoidal shape due to positional relationship between the projector and the projection surface. For correcting this distortion, keystone correction which corrects distortion of a projection image (hereinafter referred to as trapezoidal distortion as well) is employed.
The keystone correction produces an image distorted in the direction opposite to the distortion direction of the projection image on the projection surface to form a transformed image (hereinafter referred to as image after transformation as well) on the liquid crystal panel. According to this method, a rectangular image is transformed into a quadrangular image such as trapezoid and parallelogram and displayed on the liquid crystal panel. Thus, the transformation ratio of the image after transformation on the liquid crystal panel to the original image differs according to the positions on the image after transformation.
Pixel values of the image after transformation are calculated by pixel interpolation based on pixel values of the original image. In calculating the pixel values of the image after transformation according to related art, interpolation is performed using the same filter coefficient for the entire image. In this case, image quality decreases at the portion having high transformation ratio. For overcoming this problem, such a technology has been proposed which changes the filter coefficient according to the projection angle to the projection surface of the projector and the coordinate position on the liquid crystal panel.
According to an image processing device disclosed in JP-A-2005-12561, the filter coefficient is varied according to the projection angle to the projection surface of the projector and the coordinate position on the liquid crystal panel. In this case, a table of filter coefficients for respective projection angles to the projection surface of the projector needs to be prepared, for example. That is, the filter coefficient is calculated based on the two parameters of the projection angle to the projection surface of the projector and the coordinate position on the liquid crystal panel. Thus, algorithms for the calculation become complicated.
These problems arise not only from the case of projector but also from other image processing devices which can transform images.